This invention relates generally to gas turbine engine tailpipes.
Most non-thrust producing gas turbine engines, such as those used on helicopters, have attached at the exhaust of the engine a diffusion tailpipe. This tailpipe lowers the back pressure at the last stage turbine and also lowers the exhaust gas velocities to eliminate exhaust plume impingement issues on downstream components.
Typically, these engines also produce exit swirl at off-design power conditions. The traditional method for straightening the exhaust flow, prior to diffusing, is the use of exit guide vanes (EGV). Gas turbine engines are required to traverse a wide range of power settings throughout a standard duty cycle. This large traversal causes the exhaust exit swirl to xe2x80x9cswingxe2x80x9d from large positive angles to large negative angles where a zero angle is axially straight from the exhaust of the gas turbine engine. Because the swirl angle varies so significantly throughout the operating envelope, a fixed EGV system would be acceptable for only one power setting and introduce a significant increase in system losses at all other settings. Also, a variable EGV system is heavy, costly and increases maintenance requirements.
Accordingly, there is a need for a gas turbine engine tailpipe that effectively eliminates the swirl of the exhaust gas from the engine, diffuses the exhaust gas flow and diminishes its exit velocity for the entire range of swirl angles.
An object of the present invention is to provide a gas turbine engine tailpipe that effectively eliminates the swirl of the exhaust gas from the engine, diffuses the exhaust gas flow and diminishes its exit velocity for the entire range of swirl angles.
The present invention meets this objective by providing a tailpipe for a gas turbine engine having a cylindrical portion and lobed portion. The lobed portion extends a length X and has a plurality of circumferentially disposed peaks and valleys. Over at least the first 30 percent of length X, the radius of each valley is greater than the radius of each peak and is greater than 10 percent of the equivalent diameter DE. Also, the effective flow area at the end of the lobed portion is greater than the effective flow area at its beginning growing gradually at safe diffusion rates. The cylindrical portion includes a straight portion and a canted portion.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.